Stabilised polypropylene

ABSTRACT

A polypropylene composition comprises: (a) a first stabilising component consisting of 100 ppm or less based on the weight of the polypropylene of a phenolic antioxidant or a mixture of phenolic antioxidants; (b) a second stabilising component consisting of 500 to 1000 ppm based on the weight of the polypropylene of a phosphite antioxidant or a mixture of phosphite antioxidants; and optionally (c) a third stabilising component consisting of 100 ppm to 5000 ppm based on the weight of the polypropylene of a hindered amine light stabiliser or a mixture of such stabilisers. The polypropylene composition advantageously is in the form of fibres. A preferred phenolic antioxidant is 1,3,5-tris(4-tert-butyl-3-hydroxy-2,6 dimethylbenzyl)-1,3,5-triazine-2,4,6-( 1 H, 3H, 5H)-trione (Lowinox 1790). A preferred phosphite antioxidant is tris(2,4-di-t-butylphenyl) phosphite (Alkanox 240). A preferred optional hindered amine light stabiliser is dimethyl succinate polymer with 4-hydroxy-2,2,6,6-tetramethyl-1-piperidine (Lowilite 62).

This invention relates to stabilised polypropylene compositions, moreparticularly but not exclusively to stabilised polypropylene fibres.

Polypropylene (PP) fibres have a wide field of application includinggeo/agro textiles, curtains, diapers, medical clothing, tissues, largebags and nets.

All these applications need the PP to be stabilised in order to survivesevere extrusion and spinning processes, which are usually performed attemperatures between 245° C. and 300° C. Process stabilisation isusually obtained by the addition to the PP of stabiliser mixtures ofphenolic antioxidants and phosphite antioxidants. Sometimes, also,stability of the PP fibres to light is required and when this is thecase, UV stabilisers are added, for example hindered amines. These UVstabilisers sometimes also are necessary for LTHA requirement.

The properties to be maintained in PP fibres are:

-   -   viscosity (measured as MFI—Melt Flow Index).    -   colour during processing (measured as YI—Yellowness Index).    -   colour during exposure to NO_(x) gases (gas fading) which are        usually formed domestically by the combustion of propane and        butane.

The required properties are generally provided by phenolic antioxidants,which preserve the PP from degradation during processing, in combinationwith phosphites which are known to enhance the effectiveness of thephenolic antioxidants by heterolytic decomposition of hydroperoxidesformed into the polymer at high temperature and in the presence of air(oxygen). This enhancement of phenolic antioxidant effectiveness byphosphites is known as “synergistic effect”.

Even though phenolic antioxidants offer good process stabilisation ofPP, most phenolic antioxidants exhibit the disadvantage of yellowing(YI) due to their oxidation to coloured quinones by air or NO_(x) gases.

Only a limited number of phenolic antioxidants offer an acceptablebalance of all the required properties, such as for example Lowinox1790—1,3,5-tris(4-tert-butyl-3-hydroxy-2,6dimethylbenzyl)-1,3,5-triazine-2,4,6-(1H,3H,5H)-trione; Irganox1425—calcium diethylbis (CC3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl)methyl) phosphonate), Anox IC-14 (1,3,5-tris(3,5-di-t-butyl-4-hydroxybenzyl) isocyanurate) and Anox 20Tetrakismethylene (3,5-di-t-butyl-4-hydroxyhydrocinnamate) methane.

All of these acceptable phenolic antioxidants are used at quite a highlevel of concentration, ranging from 500 to 1500 ppm and in combinationwith phosphites at ratios from 1:1 to 1:4 (phenol:phosphite).

Quite recently there has appeared on the market some “phenol free”formulations where the phenolic components have been substituted by abenzofuranone or a dialkylhydroxylamine. Even though these new systemsoffer some advantages over the old systems, they still show somedisadvantages. For example, PP used in fibre spinning must have a lowviscosity and because the PP coming out from the polymerisation reactorshas a MFI between 2 and 12, it is necessary to “degrade” the PP duringextrusion by breaking the long polymeric chains to shorter chains andthis is achieved by introduction of special peroxides during extrusion.The PP obtained is called “controlled rheology PP” or “cracked PP”. Itis only in very few cases that the necessary MFI is obtained directlyfrom polymerisation and does not require the use of peroxides.

However, consumption of the aforementioned expensive peroxides dependson the nature and concentration of the stabilising system. It is wellknown that some phenolic antioxidants and some phosphites give a highlevel of peroxide decomposition with a clear impact on the cost of fibremanufacture and on byproduct accumulation into the polymer which worsensthe organoleptic properties of the same. Unfortunately, also,benzofuianones and dialkylhydroxylamines react with peroxides,destroying a portion of them and give rise, as in the case ofhydroxylamines, to coloured byproducts.

This means that none of the stabilising systems currently on the market,even though some of them are very expensive, are able to satisfy all therequirements of fibre manufacturers simultaneously. In some cases, agood MFI is accompanied by a very bad colour. In some other cases, highconsumption of peroxides for “cracked PP” is obtained, or “gas fading”properties are very poor. Fibre manufacturers, therefore, are obliged toselect and use different formulations with regard to the most importantproperties required for the final PP application, whereas theirpreference would be to have just one formulation valid for allapplications they might want

In addition to all the above considerations, it has to be borne in mindthat in some PP fibre applications, e.g. diapers and clothing, thefibres come into contact with human skin. It is well known thatextractability of stabilisers from plastics depends on the chemicalnature of the stabilisers and from their concentration (gradienteffect). The higher the concentration of the stabiliser, the higher isthe probability of stabilisers being absorbed through the skin. Itfollows that decreasing the overall concentration of stabilisers in thePP fibres offers a very positive impact on health and also on cost.

We have surprisingly found that particular PP stabiliser formulationswith very low phenolic concentration can provide very good processingstabilisation (MFI), very low discolouration (YI) and very low gasfading, similar to or better than the performance obtained by the abovementioned “phenol free” systems and with the advantage of lowinterference with peroxides used in controlled rheology applications.

According to the present invention, there is provided a polypropylenecomposition which comprises:

-   -   (a) a first stabilising component consisting of 100 ppm or less        based on the weight of the polypropylene of a phenolic        antioxidant or a mixture of phenolic antioxidants;    -   (b) a second stabilising component consisting of 500 to 1000 ppm        based on the weight of the polypropylene of a phosphite        antioxidant or a mixture of phosphite antioxidants; and        optionally    -   (c) a third stabilising component consisting of 100 ppm to 5000        ppm based on the weight of the polypropylene of a hindered amine        light stabiliser or a mixture of such stabilisers.

Preferably, the polypropylene composition comprises 100 to 50 ppm of thephenolic antioxidant or mixture of phenolic antioxidants.

In a preferred embodiment of the invention the polypropylene compositionis in the form of polypropylene fibres.

The phenolic antioxidant preferably is a less hindered phenol, i.e. aphenol which has some steric hindrance, but not at the high level ofsteric hindrance of the more common antioxidants based on2,6-di-t-butylphenol.

Further preferably, the hindered phenol antioxidant is selected from atleast one of 1,3,5-tris(4-tert-butyl-3-hydroxy-2,6dimethylbenzyl)-1,3,5-triazine-2,4,6-(1H, 3H,5H)-trione (Lowinox 1790); 2,2′-methylenebis(6-t-butyl-4-methylphenol)(Lowinox 22 M46); 4,4′-butylidenebis (2-t-butyl-5-methylphenol) (Lowinox44B25); 2,2′-isobutylidenebis(4,6-dimethylphenol) (Lowinox 22IB46); and1,1,3-tris(2′-methyl-4′-hydroxy-5′-t-butylphenyl)butane (Lowinox CA22);2,5-Di-t-amylhydroquinone (Lowinox AH25);2,2′-Methylene-bis(4-methyl-6-(1-methyl cyclohexyl) phenol (LowinoxWSP); 4,4′-Thiobis (2-t-butyl-5-methylphenol) Lowinox TBM6; 2,2′-Thiobis(6-t-butyl-4-methyl phenol) Lowinox TBP6; and Triethylene glycol bis[3-(3-t-butyl-4-hydroxy-5-methylphenyl) propionate] (Lowinox GP45).

The phosphite antioxidant preferably is selected from at least one oftris(2,4-di-t-butylphenyl)phosphite (Alkanox 240),bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite (Alkanox P-24); andtetakis (2,4-di-butylphenyl)-4,4′biphenylene diphosphonite (Alkanox24-44), and bis (2,4-dicumylphenyl) pentaerythritol diphosphite(Doverphos S-9228).

The hindered amine light stabiliser preferably is selected from at leastone of dimethyl succinate polymer with4-hydroxy-2,2,6,6-tetramethyl-1-piperidine ethanol (Lowilite 62);poly((6-((1,1,3,3-tetramethylbutyl)amino)-s-triazine-2,4diyl)(2,2,6,6-tetramethyl-4-piperidyl)imino)hexamethylene (2,2,6,6-tetramethyl-4-piperidyl)imino))) (Lowilite 94);and N^(I), N^(II), N^(III), N^(IV)-tetrakis(2,4-bis(N-1,2,2,6,6-pentamethyl-4-piperidyl)-n-butylamino)-1,3,5-triazin-6-yl)-4,7-diazadecane-1,10-diamine(Chimassorb 119).

The preferred ratio of phenolic antioxidant to phosphite antioxidant inthe polypropylene composition is in the range 1:10 to 1:20 by weight

The present invention is also a process for stabilising a polypropylenecomposition which comprises incorporating in said polypropylenecomposition at least one mixture comprising a component (a), a component(b) and optionally a component (c) as defined above.

From another aspect, the present invention is also the use of astabilising formulation comprising at least one mixture of a component(a), a component (b) and optionally a component (c) as defined above forstabilising a polypropylene composition.

From yet another aspect, the present invention is also a stabilisingformulation for polypropylene compositions comprising at least onemixture of a component (a), a component (b) and optionally a component(c) as defined above.

The prior art teaches that up to a certain level, the greater theconcentration of phenolic antioxidant the better the MFI performancewhereas the present invention teaches that very good MFI performance canbe obtained at very low levels of phenolic antioxidant.

Furthermore, the prior art teaches that the optimum ratio for phenolantioxidant to phosphite antioxidant is within the range of 1:1 to 1:4by weight The present invention however shows that a ratio of phenolicantioxidant to phosphite antioxidant of 1:10 to 1:20 by weight givesbeneficial advantages from health, environment and cost aspects.

The two and three component blends of the present invention providestabiliser packages which give unexpectedly good results inpolypropylene fibre applications.

The stabiliser blends of the invention offer unique improved performanceover current state of the art stabilising systems and offer similar tobetter processing stability, better to similar colour stability, bettergas fading performance and on top of this lower interaction withperoxides in controlled rheology grades. This combination of propertiesis highly desired for high-end polypropylene fibre applications.FiberPlus, Lowinox, Alkanox, Anox, Lowilite and NDB are trade marks ofGreat Lakes Chemical Corporation.

Fiberstab, Irgastab, Irganox and Chimassorb are trade marks of CibaGeigy.

Doverphos is a trademark of Dover Chemical Corporation.

Genox is a trade mark GE Speciality Chemicals.

Embodiments of the invention will now be described, simply by way ofexample.

General Description of the Preparation of the Stabiliser Blends of theInvention in Polypropylene Powder.

A) Mixing of the Additives

Mixing of the additives, which can be phenolic antioxidants, phosphiteantioxidants, hindered amine antioxidants, acid scavengers, peroxidesand others, with the polypropylene powder is done as described below anddepends highly on the physical form of the stabilisers. The additivescan be used in powder form, liquid form and in No Dust Blend (NDB) form

1. Additives in Powder Form:

50% of the polypropylene powder is weighed into a plastic bag, thepowder additives are weighed separately and added to the polypropylenepowder in the bag. The remaining polypropylene powder is then added andthe bag is blown up with nitrogen and shaken for at least 2 minutes indifferent directions.

2. Additives in Liquid Form:

The peroxide used is a liquid. As described in paragraph 1 above, 50% ofthe polypropylene powder is weighed into a plastic bag, then a smallamount of the polypropylene (which is subtracted from the totalpolypropylene amount) is then weighed in an aluminium pan. To this panwith polypropylene powder, the correct amount of peroxide is added via apipette and mixed with the polypropylene powder with a spatula for about10 minutes (or until a homogeneous powder mixture is formed). Thecontent of the aluminium pan is then added to the polypropylene powderin the plastic bag, the remaining polypropylene powder is added and thebag is blown up with nitrogen and shaken for at least 2 minutes indifferent directions.

3. Additives in NDB Form:

NDB blends are a preblend of additives without polymer carrier madeaccording to U.S. Pat. No. 5,240,642 and European Patent Application No514784. Similar blends are available from alternative suppliers whichare referred to as ‘one packs’.

When the additives are in this specific physical form, the NDB or‘one-pack’ is first powderised again by means of a mortar and pestle. Tomix the additives with the polypropylene powder the method as describedin paragraph 1 above can be followed.

B) Processing of the Additive/Polypropylene Powder Mixture

After 2 minutes shaking of the plastic bag, the mixture is poured intothe hopper of a Brabender single screw extruder (Compression ratio 3:1,LID 25, Dscrew 19 mm, screw speed 60 rpm).

When cracking of the initial melt flow is desired, the mixture is firstextruded using the following settings on the Brabender single screwextruder

-   -   Temperature profile: 200-215-235-250° C.    -   1 extrusion pass under nitrogen blanket

When no cracking is desired, no peroxide is added to the system but themixture is extruded on the Brabender single screw extruder using theabove mentioned settings. Strands are collected and pelletised. Thisfirst extrusion pass is referred to as the compounding pass or passzero.

In order to evaluate the performance of different additive formulations,the compound after pass zero, is extruded on the Brabender single screwextruder using the following settings:

-   -   Temperature profile: 200-225-250-275° C.    -   5 extrusion passes in open air.

After each extrusion pass the strands are caught up and pelletised.Pellets are collected after the 1^(st), 3rd and 5^(th) extrusion passfor further measurements (colour measurements, melt flow measurements)whereas anti gas fading resistance is measured on fibers.

C) Testing of the Performance of Different Formulations

Measuring the Yellowing Index (YI) on pellets, which are collected afterthe 1st, 3rd and 5th extrusion pass determines the colour stability of aformulation. Yellowing index is measured according to standard ASTME313.

Measuring the melt flow (MFI) on pellets, again collected after the1^(st), 3^(rd) and 5^(th) extrusion pass determines the processingstability of a formulation. The melt flow is measured according tostandard ISO 1133.

Gas fading resistance is measured on film or fibre samples and measuresthe yellowing of a formulation in the presence of NOx gases. Gas fadingresistance is an important property for polypropylene fibreapplications. During storage the fibres are often exposed to NOx gasesand given the high surface to volume ratio of polypropylene fibresespecially fine denier fibres are sensitive to this discolourationphenomena Gas fading resistance is tested by measuring Delta E accordingto AATCC method 23.

In the following Examples, stabiliser formulations/systems areidentified as follows:

FiberPlus NC is a two component formulation of the invention —[1:10]Lowinox 1790/Alkanox 240.

FiberPlus LT is a three component formulation of the invention[1:10]—Lowinox 1790/Alkanox 240+Lowilite 62.

FiberPlus LL is a three component formulation of the invention —7%Lowinox 1790+70% Alkanox 240+23% Lowilite 62.

FiberPlus HL is a three component formulation of the invention —6.5%Lowinox 1790+65% Alkanox 240+28.5% Lowilite 94.

Fiberplus BW is a three component formulation of the invention —7%Lowinox 1790+70% Alkanox 240+23% Lowilite 94.

Irganox B501W and Anox IC-14/Alkanox 240 systems are examples of stateof the art phenol containing systems.

Fiberstab L112, Irgastab FS 410, Irgastab FS 210 and Genox EP/Chimassorb944 systems are examples of state of the art “phenol free” systems.

EXAMPLE 1

Example 1 relates to formulations of the invention in Spheripol PPresin.

Mixing, processing and testing of the formulations are carried out as inthe general description set forth above.

Loads are in ppm.

Extrusion is carried out at 240-275-300° C.

Table 1 below shows two and three component formulations of theinvention and state of the art formulations in non-crackedpolypropylene.

Table 2 below shows two and three component formulations of theinvention and state of the art formulations in cracked polypropylene.

Results of testing are summarised in Tables 3 to 7 below. TABLE 1Non-Cracked PP FiberPlus Irganox Fiberstab IC14/ Fiberstab SystemFiberPlus NC LT B501W L112 Alk 240 410 Load level 990 1290 2000 12001500 1200 Formulation A B C D E F CaSt - Faci S 600 600 600 600 600 600Alk 240 900 900 1000 1000 Alk P-24 Anox 20 Anox IC14 500 Lowinox 90 901790 Irganox 1425WL 1000 Fiberstab 1200 L112 Fiberstab 410 1200 Lowilite62 300

TABLE 2 Cracked PP Irganox FiberPlus FiberPlus IC14/ FiberStab SystemB501W NC LT Alk 240 410 Load level 2000 660 960 900 750 Formulation G HI L M CaSt - Faci S  500 500 500 500 500 Alk 240 1000 600 600 600 AlkP-24 Anox 20 Anox IC14 300 Lowinox  60  60 1790 Irganox 1000 1425WLFiberstab 410 750 Lowilite 62 300

TABLE 3 Repeated extrusions at 240° C.: MFI & YI MFI and YI are theaverage values of several measurements. 1st 3^(rd) 5th Formulation MFIYI MFI YI MFI YI “Non cracked PP” A 10.71 −2.48 11.19 −2.57 11.11 −2.06B 10.96 −2.51 11.39 −1.86 11.23 −1.31 C 11.96 −2.17 12.53 −1.42 13.13−0.73 D 12.21 −3.24 12.94 −1.54 13.99 −0.79 E 10.66 −2.57 11.51 −1.5511.78 −0.19 F 11.35 −2.07 12.86 −0.77 14.32 0.24 “Cracked PP” G 19.17−2.63 19.96 −2.08 20.36 −1.77 H 17.75 −2.14 18.66 −1.37 20.01 −0.41 I16.67 −1.99 17.62 −1.64 18.76 −0.63 L 16.95 −1.43 17.91 0.03 19.41 1.39M 17.6 −1.93 19.69 −1.45 21.26 −1.04

Both in “cracked” and “non cracked” PP formulations of the invention Hand I show the best MFI and comparable YI vs the “traditional” (G) and“state of the art” (L,M,) formulations. TABLE 4 Repeated extrusions at275° C.: MIFI & YI MFI and YI are the average values of severalmeasurements 1st 3rd 5th Formulation MFI YI MFI YI MFI YI “Non crackedPP” A 11.26 −2.18 12.29 −0.62 13.06 0.86 B 11.48 −2.24 12.31 −0.63 13.410.72 C 12.68 −2.71 13.87 −2.05 15.03 −0.89 D 11.75 −2.01 12.74 −1.1413.79 −0.41 E 11.53 −2.15 12.15 −1.25 13.08 0.37 F 11.68 −1.54 13.81−0.06 16.31 1.23 “Cracked PP” G 20.18 −2.18 21.51 −1.29 22.76 −0.42 H18.52 −2.08 20.22 −1.41 22.55 −0.69 I 17.73 −1.78 19.62 −1.52 21.69−0.88 L 17.78 −1.2 19.43 0.15 21.64 1.29 M 18.21 −2.02 20.13 −1.01 22.210.15

Formulations of the invention H and I show the best YI and a comparableMFI vs “traditional” (G) and “state of the art” (L,M) formulations.TABLE 5 Repeated extrusions at 300° C.: MFI & YI MFI and YI are theaverage values of several measurements “Non cracked PP” 1^(st) 3^(rd)5th Formulation MFI YI MFI YI MFI YI A 12.09 −2.39 15.11 −1.88 19.87−1.41 B 11.76 −2.18 14.53 −0.74 17.57 0.81 C 13.64 −2.76 17.17 −2.0520.18 −1.41 D 12.82 −1.43 14.44 −0.44 16.27 0.62 E 12.54 −1.73 14.78−0.37 17.82 0.71 F 12.02 −0.82 15.05 1.27 20.79 2.66

“Cracked PP” 1^(st) 3^(rd) 5th Formulation MFI YI MFI YI MFI YI G 21.42−1.79 24.51 −1.24 27.13 −0.38 H 19.95 −1.87 24.72 −1.34 29.92 −0.43 I18.91 −1.66 23.33 −0.81 28.68 −0.15 L 18.91 −0.52 23.61 0.68 28.32 1.73M 18.85 −1.44 22.23 0.19 26.61 1.75

Formulation of the invention (I) shows a good MFI at the 5th extrusion,similar to “state of the art” L but much better in YI; both H and I arebetter than L and M both for MFI and YI TABLE 6 Colour measurementEquipment: Macbeth Colour Eye 3000 Reflection ASTM E 313 Standard: Lightsource: ID65 Specimen: PP fibers Test: gasfading (as Delta E) “NonCracked PP” Formulation Time (h) Cycles A B C D E F 0 0 0 0 0 0 0 20 10.57 0.43 2.55 0.55 0.69 0.42 43 2 0.66 0.49 4.21 0.67 0.74 0.48 65.5 30.73 0.58 5.46 0.91 1.51 0.64 86.5 4 0.83 0.65 6.25 1.01 1.82 0.87 107.55 0.83 0.65 6.73 1.08 1.98 0.86 128.5 6 0.85 0.71 7.12 1.13 2.18 0.96

Formulations of the invention A and B show the best values for gasfadingvs both “traditional” (C,E) and “state of the art” (D,F) formulations.“Cracked PP” Formulation Time (h) Cycles G H I L M 0 0 0 0 0 0 20 1 1.350.25 0.19 0.27 0.14 43 2 2.66 0.38 0.23 0.35 0.19 65.5 3 3.77 0.47 0.290.58 0.29 86.5 4 4.41 0.53 0.34 0.81 0.34 107.5 5 4.81 0.53 0.38 0.850.47 128.5 6 5.21 0.55 0.39 0.99 0.48

Formulations of the invention, H and I, are the best, together withformulation M which however is one of the worst for YI during extrusion(see Table 5). TABLE 7 Peroxide Consumption (Peroxide necessary (in ppm)to crack PP) from MFI 2.05 to MFI I8) Formulation Ppm G 450 H 426 I 406L 406 M 472

Formulation M, considered to be the “state of the art” for PP fibers,shows the highest peroxide consumption.

The above results confirm that the exemplified formulations of theinvention show, both in “non cracked” and “cracked” Spheripol PP, thebest balance among the performances required in PP fibers when comparedwith both the older and newer stabilizing systems, providing in this wayto the users a single formulation satisfying the requirements of alltheir end applications in addition to giving cost savings.

EXAMPLE 2

Example 2 relates to FiberPlus formulations of the invention in othertypes of PP resins.

Tables 8 and 9 below show data and test results for FiberPlus NC and the“phenol free” system Irgastab FS410 in cracked PP (EI Paso/Rexenetechnology, MFI 30). TABLE 8 NC FS410 Alk 240 600 Low 1790 60 FS410 800Acid Scavenger 650 650

TABLE 9 Formulation NC FS410 MFI Pass1 33.44 34.24 Pass 5 51.27 47.39 YIPass 1 0.66 1.13 Pass 5 4.57 3.98 Gasfading 0.388 0.459 DE 6 cyclesPeroxide 375 445 consumption

FiberPlus NC shows lower peroxides consumption, better gasfading andcomparable YI when tested against the Irgastab FS 410 “phenol free”system

Table 10 below shows data of FiberPlus systems and state of the artsystems in non-cracked BP/Amoco Slurry PP and Table 11 shows the resultsof testing these systems.

-   Resin: non-cracked PP, BP/Amoco Slurry technology, MFI 12

Test: Multipass extrusion at 275° C. measuring MFI and YI on pellets.TABLE 10 State of the Art System FiberPlus system Genox LL HL BW FS L112 FS 410 EP/944 B501W CaSt 250 250 250 250 250 250 250 Alk 240 900 900900 Low 1790 90 90 90 LL 62 300 LL 94 600 300 600 Genox EP 600 FS 4101200 FS L 112 1200 B501W 2000

TABLE 11 MFI Pass 12.57 13.04 12.93 12.91 13.58 13.28 13.62 1 Pass 15.0615.98 15.99 15.05 17.71 16.85 15.87 5 YI Pass −1.764 −1.857 −2.083−1.819 −0.924 −1.297 −1.775 1 Pass 0.678 1.107 0.286 −0.101 1.293 1.0870.967 5

The data in Table 11 shows that FiberPlus systems have similar MFI tostate of the art systems. Also, each FiberPlus system is able to matchthe colour of its comparable state of the art system

Table 12 below shows data of FiberPlus systems and state of the artsystems in cracked BP/Amoco Slurry PP and Table 13 shows the results oftestings these systems.

-   Resin:    -   cracked PP BP/Amoco Slurry technology, MFI 12.

cracking from 2 to 28-29 with Trigonox 101 as free-radical source. TABLE12 State of the Art Systems FiberPlus system Genox LL HL BW FS L 112 FS410 EP/944 B501W CaSt 250 250 250 250 250 250 250 Alk 240 600 600 600Low 1790 60 60 60 LL 62 300 LL 94 400 300 400 Genox EP 400 FS 410 800 FSL 112 1200 B501W 2000

TABLE 13 Peroxide Consumption [ppm] 640 640 640 855 710 690 655 MFI Pass29.99 30.38 29.75 29.1 28.89 30.82 30.57 1 Pass 36.05 35.74 34.68 32.5736.9 36.44 33.49 5 YI Pass −2.070 −1.832 −2.079 −2.099 −1.769 −2.020−1.882 1 Pass −0.489 −0.258 −0.165 −0.579 −0.325 −0.049 0.402 5

The data in Table 13 shows that FiberPlus systems offer the followingadvantages against state of the art systems.

-   (a) lower peroxide consumption and thus lower peroxide interaction    than state of the art “phenol free” systems.-   (b) processing performance for each FiberPlus system which matches    the processing performance of its comparable state of the art    systems.

EXAMPLE 3

Example 3 relates to experiments (i) using a phosphite alone and (ii)using a different phosphite from that used in Examples 1 and 2.

The experiment where Alkanox 240 is replaced by Alkanox P-24 is to showthat different phosphites can be used in the stabiliser formulations ofthe invention

The systems were tested at 1000 ppm in non-cracked PP(Spheripoltechnology, MFI 12) and were tested against 1000 ppm [1:2] Anox20/Alkanox 240 as reference.

The data is summarised in Tables 14 and 15 below. TABLE 14 1790/P-24 24020/240 CaSt 500 500 500 Low 1790 100 Alk 240 1000 500 Anox 20 500 AlkP-24 900

TABLE 15 1790/P-24 240 20/240 MFI Pass 1 11.1 13.7 12.6 Pass 5 12.2 21.016.3 YI Pass 1 −1.72 −2.07 −0.58 Pass 5 5.35 1.3 7.87

The results show that Lowinox 1790/Alkanox P-24 of the invention,compared against state of the art Alkanox 240/Anox 20, exhibits betterMFI and YI. The results also show how the addition of a small quantityof Lowinox 1790 improves MFI when compared with Alkanox 240 alone.

EXAMPLE 4

Example 4 relates to experiments using different low hindered AO's withAlkanox 240 system.

The purpose of the experiments is to show that other low hinderedphenols can be used in stabiliser formulations of the invention. TABLE16 CaSt 500 500 500 Lowinox CA22 10 100 Low 1790 90 90 Alk 240 900 900900

TABLE 17 1790/240 1790/240/CA22 CA22/240 MFI Pass 1 12.51 12.32 12.95Pass 5 15.03 13.93 16.58 YI Pass 1 3.97 4.71 4.39 Pass 5 23.32 20.9420.97

The results of Table 17 show in column 3 that adding Lowinox CA22 insmall amounts to Alkanox 240 provides similar results as adding Lowinox1790 to Alkanox 240 (column 1) for MFI and YI but column 2 shows thatMFI is better still when a blend of Lowinox CA22/Lowinox 1790 is used ina ratio of 1:9. Two “low hindrance” phenols therefore show unexpectedsynergy.

EXAMPLE 5

Example 5 relates to experiments with variable amounts of HALS.

The purpose of the experiments is to check the performance of FiberPlussystems with increased HALS level against state of the art systems.

-   Resin: Non-cracked PP (BP/Amoco Slurry, MFI 12)-   Tests:    -   MPE measuring MFI (ISO 1133) and YI/ASTME313) on pellets    -   Gasfading on films [AATCC method 23]

UV test on films [SAEFJ1885] TABLE 18 FiberPlus NC + 250-2000 ppm LL62CaSt 250 250 250 250 250 Low 1790 90 90 90 90 90 Alk 240 900 900 900 900900 LL 62 250 500 1000 1500 2000 LL 94 Chim 119

TABLE 19 MFI Pass 1 12.57 12.52 12.42 12.42 12.42 Pass 5 15.06 14.514.91 14.76 14.46 YI Pass 1 −1.764 −2.003 −1.997 −1.790 −1.597 Pass 50.678 0.941 0.536 1.030 1.163 Gasfading 6 cycles YI 2 2 2 2 2 Gray scale5 4-5 5 5 5

TABLE 20 FiberPlus NC + 250-2000 ppm LL94 CaSt 250 250 250 250 250 Low1790 90 90 90 90 90 Alk 240 900 900 900 900 900 LL 62 LL 94 250 500 10001500 2000 Chim 119

TABLE 21 MFI Pass 1 12.73 12.89 12.97 12.92 12.81 Pass 5 14.98 15.2215.18 15.55 15.83 YI Pass 1 −1.771 −1.904 −1.544 −1.650 −1.363 Pass 50.494 0.884 1.686 −0.176 2.335 Gasfading 6 cycles YI 2 2.1 2.1 2.1 2.2Gray scale 4-5 5 5 4-5 4-5 UV (tensile properties) SAEJ 1885 22 28 45 49NM E50

TABLE 22 FiberPlus NC + 250-2000 ppm Chim 119 CaSt 250 250 250 250 250Low 1790 90 90 90 90 90 Alk 240 900 900 900 900 900 LL 62 LL 94 Chim 119250 500 1000 1500 2000

TABLE 23 MFI Pass 1 12.58 12.78 12.86 13 12.83 Pass 5 14.54 14.88 15.7715.69 15.71 YI Pass 1 −1.737 −1.653 −1.550 −1.551 −1.549 Pass 5 0.8280.774 1.345 1.733 1.902 Gasfading 6 cycles YI 2.5 2.1 2.5 2.1 2.1 GrayScale 4-5 5 4-5 5 5 UV (tensile properties) SAEJ 1885 28 32 37 81 78 E50

EXAMPLE 6

Example 6 relates to using Anox 20 and a HALS at higher concentrations.

Anox 20/Lowilite 94 synergy generated at 1000 ppm in non-cracked PP(BP/Amoco Slurry technology)

-   Resin: BP/Amoco Slurry PP, non-cracked, MFI 12.

Test: Multiple pass extrusion measuring MI and YI on pellets. TABLE 24FiberPlus HL BW Anox 20 CaSt 250 250 250 250 250 250 250 250 250 Anox1000 800 600 400 200 0 500 20 LL 94 600 300 200 400 600 800 1000 Low 9090 1790 Alk 240 900 900 500

TABLE 25 MFI Pass 1 13.04 12.93 15.30 17.03 17.69 18.79 21.41 26.1613.53 Pass 5 15.98 15.99 21.66 26.89 28.71 30.85 38.75 64.34 18.10 YIPass 1 −1.857 −2.083 −0.762 −1.395 −1.380 −1.590 −1.664 −2.066 −2.581Pass 5 1.107 0.286 3.150 2.001 1.335 2.016 0.686 −0.942 0.196

Observations from the results of Examples 5 and 6:

-   (a) FiberPlus NC does not suffer from the increase of HALS    concentration as shown in the Tables, e.g. when increasing the    amount of Lowilite 62 from 250 to 2000 ppm the MFI remains good, YI    increases just a little bit and gas fading remains at the same    level. The same applies to other HALS, e.g. Lowilite 94 and    Chimassorb 119.-   (b) The results show how good are the average performances of    FiberPlus NC when compared to a “state of the art” phenol/phosphite    blend, e.g. Anox 20/Alkanox 240 where the increase of HALS    concentration and reduction of Anox 20 significantly worsens with    insignificant improvements in YL-   (c) Increase of HALS concentration increases the tensile strength of    FiberPlus NC.

1. A polypropylene composition which comprises: (a) a first stabilising component consisting of 100 ppm or less based on the weight of the polypropylene of a phenolic antioxidant or a mixture of phenolic antioxidants; (b) a second stabilising component consisting of 500 to 1000 ppm based on the weight of the polypropylene of a phosphite antioxidant or a mixture of phosphite antioxidants; and optionally (c) a third stabilising component consisting of 100 ppm to 5000 ppm based on the weight of the polypropylene of a hindered amine light stabiliser or a mixture of such stabilisers.
 2. A polypropylene composition as claimed in claim 1 which comprises 100 ppm to 50 ppm phenolic antioxidant or a mixture of phenolic antioxidants.
 3. A polypropylene composition as claimed in claim 1 or claim 2 wherein the composition is in the form of polypropylene fibres.
 4. A polypropylene composition as claimed in claim 1 wherein the phenolic antioxidant is a hindered phenol antioxidant.
 5. A polypropylene composition according to claim 1 wherein the phenolic antioxidant is selected from at least one of 1,3,5-tris (4-tert-butyl-3-hydroxy-2,6 dimethylbenzyl)-1,3,5-triazine-2,4,6-(1H,3H,5H)-trione; 2,2′-methylenebis(6-t-butyl-4-methyl phenol); 4,4′-butylidenebis(2-t-butyl-5-methyl phenol); 2,2′-isobutylidenebis(4,6-dimethyl phenol); 1,1,3-tris(2′-methyl-4′-hydroxy-5′-t-butyl phenyl) butane; 2,5-Di-t-amylhydroquinone; 2,2′-Methylenebis [4-methyl-6-(1-methylcyclohexyl) phenol; 4,4′-Thiobis (2-t-butyl-5-methylphenol); 2,2′-Thiobis (6-t-butyl-4-methylphenol) and Triethylene glycol bis (3-(3-t-butyl-4-hydroxy-5-methylphenyl) propionate.
 6. A polypropylene composition as claimed in claim 1 wherein the phosphite antioxidant is selected from at least one of tris(2,4-di-t-butylphenyl)phosphite, bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite; and tetrakis (2,4-di-butylphenyl)-4,4′biphenylene diphosphonite and bis(2,4-dicumylphenyl) pentaerythritol diphosphite.
 7. A polypropylene composition as claimed in claim 1 wherein the hindered amine light stabiliser is selected from at least one of dimethyl succinate polymer with 4-hydroxy-2,2,6,6-tetramethyl-1-piperidine ethanol; poly((6-((1,1,3,3-tetramethylbutyl)amino)-s-triazine-2,4diyl)(2,2,6,6-tetramethyl-4-piperidyl) imino) hexamethylene (2,2,6,6-tetramethyl-4-piperidyl)imino))); and N^(I), N^(II), N^(III), N^(IV)-tetrakis (2,4-bis(N-1,2,2,6,6-pentamethyl-4-piperidyl)-n-butylamino)-1,3,5-triazin-6-yl)-4,7-diazadecane-1,10-diamine.
 8. A polypropylene composition according to any claim 1 wherein the ratio of phenolic antioxidant to the phosphite antioxidant is in the range of 1:10 to 1:20 by weight.
 9. A process for stabilising a polypropylene composition which comprises incorporating in the polyolefin composition at least one mixture comprising a component (a), a component (b) and optionally a component (c) all according to claim
 1. 10. The use of a formulation comprising at least one mixture of a component (a), a component (b) and optionally a component (c) all according to claim 1 for stabilising a polypropylene composition.
 11. A stabilising formulation for polypropylene compositions comprising at least one mixture of a component (a), a component (b) and optionally a component (c) all according to claim
 1. 